Traditional industrial processes for synthetic polymer microfiber spinning can be classified as either solvent-based or melt-based. As the name implies, solvent processing involves the spinning of a polymer solution with solidification of the fiber either through coagulation in a non-solvent (wet-spinning) or solvent evaporation (dry-spinning) In contrast, melt spinning produces fibers via the spinning of molten polymer that solidifies upon cooling; drawing usually accompanies this melt-based process to induce chain orientation and enhance mechanical properties. Typically, accessing nanoscale cross-sections is difficult, where fiber diameters of only 10-20 μm are achieved with applications in the textile industry. Pushing the limits of fiber production to the nanoscale has garnered recent attention in the processing arena.
Electrospinning is perhaps the most well-known, and one of the oldest techniques for generating sub-micron fibers in lab-scale from a polymer solution, or less commonly, a polymer melt via the application of a large electric field. This charged polymer jet is subjected to electrostatic forces, which act to elongate, thin, and solidify the polymer fiber in the characteristic “whipping instability” region. Although some success has been achieved with electrospun fibers in high-value added applications, such as air filtration, topical drug delivery, and tissue engineering scaffolds, significant disadvantages are low throughput and scalability. Additionally, electrospinning necessitates large volumes of toxic solvents that must be recovered by specialized equipment to make the process viable on a large scale.
Other approaches to nanofiber fabrication have emerged, including rotary-jet spinning, gas jet blowing, melt blowing, and bicomponent fiber spinning Recent advances in rotary jet spinning have focused on a melt-based approach to nanofiber production with throughputs significantly higher than electrospinning, but improvements are ongoing to address processing complexity as it relates to broad applicability to a range of polymer systems. Melt blowing is a particularly commercially relevant and scalable technique for achieving fiber diameters on the order of tens of microns and higher; in this process, fibers are generated in-line by extrusion of a polymer through a die orifice, while a hot air jet blows down the extrudate. It is process compatible with a wide range of polymers, and is a solvent-less and environmentally-friendly manufacturing method. However, the pursuit of nanoscale fibers has been limited primarily to polypropylene for air filtration. Collectively, these limitations on nanofiber scalability increase manufacturing costs and lower productivity.
The production of continuous nanofiber has received considerable attention for drug delivery and tissue engineering applications. Incorporation of drugs and/or other biomolecules in the fiber exhibit new trend in all types of drug delivery routes, such as topical delivery, oral, intravenous, intramuscular, or inhalation usage, to reach maximum bioavailability for desired therapeutic efficacy.
Up to now, polymer fibers have been used in different applications, such as membranes, filtration, electronic sensors and reinforcing materials. Previously employed methods to produce these fibers include electrospinning of a polymer solution or melt. More specifically, the fibers were obtained by electrospinnig the polymer out of solution or the melt under high voltage. The use of this approach, however, is limited in that the proper solvents must be found and high voltage must be used, which results in high capital costs for production. Furthermore, the sizes, materials, and cross-sections of the fibers produced by electrospinning are limited. Therefore, there is a need for a process of producing polymer fibers at a reduced cost.